Extreme Amount of Moisture in my Attic | Attic Ventilation

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Attic moisture is a very common problem in cold climates.

Attic moisture - Condensation dripping from an H clip in poorly ventilated atticAttic moisture - Frost developing on roofing nails and decking in poorly ventilated attic - black mold will follow shortlyLet’s answer the attic moisture question below (from one of the website visitors): I have an extreme amount of attic moisture, I recently had my roof re-shingled and had the roofer add 2 more vents for better ventilation.

There is a build up of frost in certain areas of my roof, it has been an extremely cold winter, would lack of insulation cause this and how deep should the insulation be?

Attic moisture - Missing attic floor insulation allows heat transfer between the conditioned space of your home and the atticLack of insulation on the attic floor (house ceiling) is definitely one of the most important reasons for attic moisture resulting from migration of warm air into the attic, and moisture condensation on the roof framing / decking.

Although, properly designed attic ventilation would most likely remove this warm air before it starts elevating attic moisture levels and condensing. However, we’re still loosing expensive energy.

Attic moisture - Vents along the lower portion of the roof, one of the solutions if there is no soffit - help to maintain air circulation and remove attic moistureInstallation of additional roof vents helps to control attic moisture under one condition – they have to be distributed properly in order to maintain air circulation between the lower and upper section of the attic, or sideways (between gables). Those two additional roof vents (I’m assuming on top of the roof) won’t help much if there’s nothing or not enough vents (air intakes) along the bottom edges of your roof.

Depending on the roof design, installation of  “lower” vents could become a challenge – the best example would be a roof with no overhang /soffits to accommodate vents. In such case, attic moisture control can be performed utilizing the following 3 passive vent options:

  1. Drip edge vents installed along the bottom edge of the roof / right above the gutter
  2. A few regular vents on the roof surface, within 1/3 of the distance between the bottom and top section of the roof plane (not an ideal situation but sometimes the only one)
  3. Hip vents – the same as a ridge vent (almost)

Attic moisture - Humidistat and temperature sensor equipped attic power vent helps to remove attic moisture - condensationUnfortunately, any significant amount of snow and / or ice accumulating at the lower portion of the roof, inside the gutter (for a drip edge vent) will most likely compromise the air flow and prevent attic moisture removal. It sounds like there’s no solution… well, if you combine a humidistat controlled attic power vent, with any of the above described passive vents, you’ll have much better chance of removing attic moisture and preventing frost and condensation from building up in your attic.

The insulation issue / how deep the attic insulation should be to minimize attic moisture problem?

It all depends on your geographical location and type of the insulation installed. The most commonly used for the attic floor are blown-in types of insulation: cellulose and fiberglass.

Attic moisture - Frost and black mold covered roof decking surface, heavy condensation stains on roof framing - caused by too much insulation stuffed into the soffit and blocking soffit ventsFor attic insulation amounts and sample calculations please visit – attic ceiling insulation

You can also find more information about your attic issues (including more about attic moisture) on my website under “Attic

Please, let me know if you have any other questions, and please – take care of attic moisture and condensation issues before it gets moldy.

Search existing Q&A at: House Attic Questions

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This article was written by Dariusz Rudnicki

I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local

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